The invention relates to stoppers for vial-type tubes, in particular tubes subjected to a controlled pressure, for example evacuated tubes of blood sampling systems.
A known blood sampling system comprises an evacuated tube closed by a stopper and an open-ended needle-holder tube slidably mounted on the tube or its stopper. This needle holder carries a hollow needle having one part protruding axially from the closed end of the holder for pricking into a vein, and another part extending axially within the holder, the latter part being encased in a loose, flexible cover or sleeve. To take a blood sample, the needle is pricked into a vein and the evacuated tube displaced until the needle pierces the stopper membrane, so that blood is sucked into the evacuated tube.
However, in practice conventional blood sampling systems are often difficult to use and have shortcomings that create health hazard conditions for laboratory staff and may alter the results of some blood determinations.
Conventional stoppers usually have a shank which penetrates inside the tube neck, the shank having an externally bevelled end which is hollow to facilitate entry into the tube. As a consequence, blood particles may aggregate in recesses in the shank and when, after centrifugation, the stopper is removed these trapped particles may fall down into the centrifuged sample and alter the result of certain blood determinations.
Also, when the stopper is removed, blood particles on the shank tend to be sprayed as an aerosol, as a result of the "bouncing" effect. This is one of the main ways in which virus or bacteria contaminate laboratory staff. Handling such a stopper which has a surface smeared with blood is thus not only an unpleasant operation, but involves health hazards.
Many problems inherent to traditional evacuated tubes stem from the fact that sealing is achieved solely by the pressure of the outside wall of the stopper against the inner surface of the tube. This single sealing means serves both to prevent escape of the liquid content (blood) and penetration of air from the exterior. Removing or inserting the stopper produces instantaneous drafts of air which contribute to the aerosol effect.
Moreover, once such a stopper has been removed from an evacuated tube and the vacuum is lost, when it is reinserted in the tube it tends to be ejected as a result of compression of air in the tube. It is thus not suitable for reinsertion as a permanent closure.